Tuning the C20LET - RAM air for the LET

A 2.0 litre turbo doing a bit over 1 bar typically wants to consume 4 litres of air every two crank revolutions.
At 4K rpm that's 2000*4=8000liters/minute, more than 100liters per second. The stock airbox volume is just a few litres, so under full throttle it's emptied in less than 100milliseconds. The airbox replenishment rate then takes over, dictating the ultimate power output until the throttle is shut.
Enough said.

Here is an attempt for a RAM-air intake on the LET:

The top and bottom parts of the airbox are stock. The snorkel is from a V6 (one from an XE could also be adapted)

The intermediate pipe is a stock airbox->intercooler pipe (the reinforced one with the ribs - it fits perfectly and flows well too)

The front bit is a silicon hose, leftover from the intercooler installation. Everything recycled!

Another implementation is shown here:

It may not look too impressive, but it fits perfectly on top of the existing setup. Some ducktape is needed to cover the hole behind the tow-hook. After some black spray paint it's invisible behind the mesh (that substitutes the tow-hook cover in both cases) The camera flash makes it visible here:

It's made of 3 airduct turns from B&Q (or other similar establishments). Ducktape (and short runs of rectangular tube) keep them all together, yet retain some flexibility needed to install/remove easily. Inside it's very rigid and smooth. There are more instructions and higher resolution photos on the website of Simon Morris and his award-winning Calibra Turbo (well, it appeared in Total Vauxhall!)

The rather abrupt turns don't affect idle or low speed driving. At high speeds air piles up the front, so any vacuum in the airbox is filled promptly.

A legitimate fear might be that of rainwater entering the airbox, and contaminating the airfilter, perhaps even destroy it. Driving at motorway speeds in a downpour could well lead to a soggy filter, especially if it's a paper one. Below is the condition of the airbox and the paper filter after driving 1200 miles up in Scotland, most of it in heavy rain. Boost was kept to a minimum, though.

The bottom of the airbox doesn't look too bad, it looks like the drainholes did a good job

The upper part of the filter hasn't been breached, in fact it looks absolutely fine

The lower part of the filter is a bit dirtier than what it would have been without the cold-air intake, but nothing dramatic. These filters are so cheap that they can be changed very often.

 

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